I see some good and bad advices in the video:
Good: mark the eggs you put under the broody.
Bad: move the broody apart from the eggs to another coop. (less risk if you put a box under her in the old situation and move the broody a few days later with box, and eggs together)
Good: a spacious room where the broody and the baby chicks can stay for the first days.
Good: provide water and chick crumble near to nest box.
Bad: put more chicks under her as she hatched. Difficult job to keep 12 chicks warm. Risk of not accepting.
Bad: put the hen in a coop with a steep ladder that can cause trouble for the young chicks. Its no problem to get down, but are they smart enough to climb up? You don’t want chicks downstairs getting cold while mama is upstairs with most of her chicks.
Good: check if there a no chicks downstairs.
I have no personal experience with hatching chicks with a broody hen, which is why I linked the YouTube video so OP had a start on the subject. Appreciate your comments on the points in this video. Hope it helps the OP. I learn a lot from YouTube videos, but I have also learned that some things people say may or may not be best practice. It's always great to get feedback from people with personal experience.